Two-component diazotype composition

ABSTRACT

A TWO-COMPONENT DIAZOTYPE MEDIUM WHICH PROVIEDES, UPON EXPOSURE AND DEVELOPMENT, A NEUTRAL IMAGE WITH LOW CONTRAST IS OBTAINED BY EMPLOYING AS THE LIGHT-SENSITIVE LAYER A POLYMERIC MATRIX SUCH AS CELLULOSE ACETATE HAVING DISPERSED THERIN A LIGHT-SENSITIVE DIAZO DYE-FORMING SYSTEM COMPRISING (1) AS THE DIAZO COMPONENT, A 2,5-DIALKOXY-4-MORPHOLINOBENZENE DIAZONIUM SALT, AND OPTIONALLY A4-(DIALKYLAMINO) BENZENE DIAZONIUM SALT; (2) AS A BLUE COUPLER, AT LEAST ONE OF A 2-HYDROXY-N-(2-ALKYLPHENYL)3-NAPHTHAMIDE, AND A2-HYDROXY-N-(2,4-DIALKOXY-5-HALOPHENYL)-3-NAPHTHAMIDE; AND (3) AS A YELLOW COUPLER, AN N-SUBSTITUTED OR N,N-DI-SUBSTITUTED 1-HYDROXY-2-NAPHTHAMIDE OR A 2-ACYLAMIDO-5-ALKYLPHENOL. THE DYE-FORMING SYSTEM IS PREFERABLY STABLIZED AGAINST PREMATURE COUPLING BY THE PRESENCE OF ACID STABILIZERS SUCH AS 5-SULFOSALICYCLIC ACID.

United States Patent Ofiice 3,573,051 Patented Mar. 30, 1971 3,573,051 TWO-COMPONENT DIAZOTYPE COMPOSITION William C. Gray, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. N Drawing. Filed July 31, 1967, Ser. No. 657,077 Int. Cl. G03c 1/58, 1/54 US. C]. 96-91 12 Claims ABSTRACT OF THE DISCLOSURE A two-component diazotype medium which provides, upon exposure and development, a neutral image with low contrast is obtained by employing as the light-sensitive layer a polymeric matrix such as cellulose acetate having dispersed therein a light-sensitive diazo dye-forming system comprising (1) as the diazo component, a 2,5 dialkoxy-4-morpholinobenzene diazonium salt, and optionally a 4-(dialkylamino)benzene diazonium salt; (2) as a blue coupler, at least one of a 2-hydroxy- -(2-alkylphenyl)- 3-naphthamide, and a Z-hydroxy-N-(2,4-dialkoxy-5-halophenyl)-3-naphthamide; and (3) as a yellow coupler, an N-substituted or N,N-di-substituted l-hydroxy-Z-naphthamide or a 2-acylamido-S-alkylphenol. The dye-forming system is preferably stabilized against premature coupling by the presence of acid stabilizers such as 5-sulfosalicyclic acid.

This invention is related to photography, and is concerned particularly with a novel two-component diazotype system which, after exposure and development, provides a neutral image with low contrast.

Two-component diazotype reproduction media have long been known. These media comprise a polymeric matrix containing at least one diazo salt and at least one coupler which reacts with the diazo salt to form a dye. In addition, there may be present various other additives, such as ultraviolet absorbers, stabilizers to prevent premature coupling of the diazo salt and coupler and the like. These compositions have been generally employed as duplicating media by exposure to activating radiation, e.g., light, through an original, whereby the transmitted light decomposes the diazo salt. After exposure the film is normally treated with a basic medium, usually ammonia, to promote coupling of the undecomposed diazo salt and coupler, thereby forming a dye in the unexposed areas and producing an image corresponding to that of the original.

Initially the dyes employed in diazotype media were of various colors, such as purple, blue and the like. More recently, however, attempts have been made to devise systems which will provide a neutral, i.e., black, grey and white, image similar to that obtained with a silver halide film. In general, these latter systems employ at least two couplers, one of which, if used alone, would form a blue dye, and the other of which, if used alone, would form a yellow dye.

The earliest neutral image systems provided a developed image of very high contrast and, while generally satisfactory for reproducing line drawings and the like, were generally unsatisfactory for reproducing inter-mediate tones. Subsequently there have been developed systems which provide a reasonably accurate image of half-tone originals. It has been found, however, that these latter systems, although satisfactory for producing copies of originals, cannot be employed to provide subsequent reproductions of such copies, a problem which is particularly acute in the case of libraries and the like wherein substantial use is made of film reproductions such as microfilm and the like. For example, the original or first generation film is normally a conventional silver-based film. Because of the lower expense of diazotype media, these films are frequently used by libraries or other depositories to provide reproductions, i.e., a second generation of the original silver-based film. This sequence is frequently carried on through a third or even a fourth generation reprint. In the prior systems, although the second generation print frequently approached the quality of the silverbased, or first generation, print the third and fourth generations evidenced a progressive increase in contrast and loss of detail, which also operated to inhibit exposure latitude.

Accordingly, it is an object of this invention to provide a new light-sensitive, diazotype dye-forming system Which, upon development exhibits an improved neutral color dye image.

It is another object of this invention to provide a novel light-sensitive diazotype dye-forming system which can produce reduced contrast copies, especially subsequent to second generation copies.

Still another object of the present invention is to provide new diazotype compositions and related photographic elements which utilize the subject light-sensitive, diazotype dye-forming systems.

These and additional objects of the instant invention will become apparent from a consideration of the following specification and appended claims.

The objects of the invention described herein are accomplished with a two-component, light-sensitive azo dye forming system which is, for example, useful in diazotype reproduction media and especially diazotype photographic elements which on exposure and development provide a neutral imagewise copy which faithfully reproduces the original with improved exposure latitude through the third and even fourth generations, such azo dye-forming systems employing certain diazonium salts and yellow and blue couplers as described herein.

The diazonium salt which is employed in accordance with this invention is a 2,5-di-lower-alkoxy-4-morpholinobenzene diazonium salt as represented by the formula:

wherein each R is a lower alkyl radical, preferably of from 1 to 2 carbons, and especially ethyl, and Z is as defined above.

The blue coupler which is employed in accordance with this invention is a Z-hydroxy-N-(2-loweralkoxyphenyl)-3- naphthamide of the formula:

wherein R is a lower alkoxy radical, preferably of from 1 to 2 carbons, and especially methoxy.

I admixture with, or in lieu of, the blue coupler of Formula III there can be employed a 2-hydroxy-N-(2,4-

(III) dilower-alkoxy--halophenyl) 3 naphthamide blue coupler of the formula:

/\ I... K/ CONH- wherein each R is a lower alkoxy radical, preferably of from 1 to 2 carbons, and especially methoxy and X is a halogen atom, preferably chlorine.

The yellow coupler which is employed in accordance with this invention can be a 1-hydroxy-N-substituted-Z- naphthamide as represented by the formula:

NI-ICOR wherein R and R each are a lower alkyl radical, preferably having from 1 to 2 carbons, and especially methyl.

The lower alkoxy and alkyl radicals in the above described diazonium salts and couplers can suitably have 1 to 8 carbon atoms and more generally have 1 to 4 carbon atoms. Lower alkylene radicals are those suitably having from 1 to 6 carbon atoms with from 1 to 4 carbon atoms being preferred.

To achieve neutral images which faithfully reproduce an original, even through a third or fourth generation copy, it has been found that the proportions of diazo salt and blue and yellow couplers are only susceptible of moderate variation. As noted above the presence of a diazo salt of Formula II is optional; however, when present it should be employed in a less than equimolar ratio in relation to the salt of Formula I, with the preferred ratio of diazo salt I to diazo salt II being in the range of from about 1:1 to about 3:1.

The relative proportion of blue coupler IV to blue coupler III, when both are present can be widely varied although a molar ratio of from about 1.521 to about 2:1 is generally preferred. On the other hand, the ratio of blue coupler to yellow coupler should be kept within rather narrow limits. When a naphthamide of Formula V is employed as the yellow coupler the molar ratio of the combined moles of blue coupler to yellow coupler should be from about 1.5 :1 to about 2.5:1, with a molar ratio of from about 1.75:1 to about 1.95:1 being preferred. When an alkanoylarnidophenol of Formula VI is employed as the yellow coupler, however, the molar ratio of blue to yellow coupler is desirably from about 0.511 to about 1.5:1, with a ratio of from about 0.9:1 to about 1.1:1 being particularly preferred.

Finally, the ratio of total moles of blue and yellow coupler to the total moles of diazo salt should be at least 1:1, with best results being obtained when the ratio is in the range of from about 1:1 to about 1.5:1 and more particularly at a ratio of from about 1.1:1 to about 1.3:1. Higher coupler concentration is possible, but not preferred due to the unnecessary excess of unreacted coupler.

The choice of which diazo salt, blue coupler and yellow coupler is to be employed in the dye-forming system of this invention is governed by the properties desired in the diazotype medium. In general, formulations containing a naphthamide of Formula V are useful in the conventional dry ammonia developers, whereas those employing an acylamidophenol of Formula VI are particularly useful in high pressure anhydrous ammonia developers, such as those disclosed in British Pat. No. 1,043,836.

In the embodiment in which the naphthamide of Formula V is the yellow coupler, the speed and color balance of the diazo film is dependent upon the presence or absence of a diazo salt of Formula II. Thus, although a relatively slower film is obtained when salts of this type are present, the film is particularly valuable when a completely neutral image is essential. On the other hand, omission of the diazo salt of Formula II, although providing a faster film, results in a product which tends to give a somewhat colored (blue) image. In this embodiment, the blue coupler of Formula IV is not employed unless the diazo salt of Formula II is present.

When an alkanoyl amidophenol of Formula VI is employed as the yellow coupler, the diazo salt is desirably that of Formula I, whereas the blue coupler is desirably that of Formula IV.

The dye-forming components described above are generally employed in the form of a film in which the components are dispersed in a polymeric matrix which is coated upon a suitable support. Typical matrix polymers are cellulose esters such as cellulose acetate, cellulose butyrate and cellulose acetate-butyrate, and also vinyl polymers like poly(vinyl acetate), poly(vinylidene chloride) and poly(vinyl butyral). Another typical polymer is 4,4'-isopropylidene-diphenyl-2-hydroxy 1,3 propylene ether. Similarly, the concentration of the dye-forming components in the polymeric matrix is not narrowly restricted, although concentrations of from about 20 to about 40 parts by weight per parts of matrix polymer are normally employed, with concentrations in the range from about 25 to about 35 parts per 100 parts being preferred.

In addition to the dye-forming components, the polymeric matrix can also contain other additives to modify the properties of the film, such as ultraviolet absorbers, stabilizers and the like. A preferred class of additives comprises the known acid stabilizers which prevent premature coupling of the azo salt and the coupler. These acid stabilizers include organic acids such as 5-sulfosalicyclic acid and the like. In general, organic acids are preferably present in all of the formulations of this invention, with the amount normally varying from about 1 to 6, and preferably from about 2 to about 5 parts by weight per 100 parts of polymeric matrix. In addition, when a diazo salt of Formula II above is present, it is preferred that a metal salt, preferably zinc chloride, be present as a dye brightener or development accelerator, generally in an amount varying from about 0.5 to about 2 parts, and preferably from about 1 to about 1.5 parts, by weight per 100 parts of matrix polymer.

A second, and especially desirable, class of additives to the compositions of this invention are hindered phenols containing, in the 2-position, either an alkyl or a cycloalkyl radical and, in the 4-position, either an alkyl radical, an alkoxy radical, a hydroxyl radical or a thioether radical which with the hindered phenolic moiety completes a hindered bisthiophenol and more generally a symmetrical bisthiophenol.

Typical useful hindered phenols employed herein include those having the formulas:

wherein each of R through R is an alkyl radical; each of R and R is either a hydrogen atom or an alkyl radical; R is either a hydroxyl radical, an alkyl radical or an alkoxy radical; R is either an alkyl radical or a cycloalkyl radical; and R is a lower alkylene radical.

As comprehended herein, an alkyl radical is a straight or branched chain alkyl radical having from 1 to about 18 carbon atoms' Typical such alkyl radicals are, for example, methyl, ethyl, isopropyl, tert-butyl, tert-octyl, dodecyl, tetradecyl and the like. Cycloalkyl radicals as described herein are saturated monovalent carbocyclic radicals having 4 to 6 nuclear carbon atoms, such as cyclobutyl, cyclopentyl, cyclohexyl, l-methylcyclohexyl and the like radicals. Alkoxy radicals as defined herein are straight or branched chain alkoxy radicals having from 1 to about 18 carbon atoms. Illustrative alkoxy radicals are methoxy, carboxymethoxy, ethoxy, butoxy, octoxy, dedecoxy, tridecoxy, a-ethoxycarbonyltridecoxy and the like. Lower alkyl and alkoxy radicals herein are typically straight or branched chain alkyl or alkoxy radicals having from 1 t0 8 carbon atoms with from 1 to 4 carbon atoms being preferred. Typical such radicals are, for example, methyl, methoxy, ethyl, ethoxy, propyl, isopropyl, propoxy, tert-butyl, butoxy, octyl, octoxy, etc. Lower alkylene radicals as noted herein are alkylene radicals having from 1 to 4 carbon atoms, such as methylene, ethylene, propylene and butylene.

Particularly useful hindered phenols employed in the subject invention include compounds of the formula:

wherein R is an alkyl radical and preferably a tertiary alkyl radical having 4 to 8 carbon atoms; R is either a hydroxyl radical, an alkyl radical or an alkoxy radical; and R is (1) a hydrogen atom when R is an alkyl radical, (2) an alkyl radical when R is a hydroxyl radical and (3) either a hydrogen atom or an alkyl radi 6 cal when R is an alkoxy radical; compounds of the formula:

wherein each of R to R is an alkyl with R and R preferably being methyl radicals and R is either a hydrogen atom or an alkyl radical; compounds of the formula:

i 2u "R21 wherein R is an alkyl radical, R is either an alkyl radical or a cycloalkyl radical and R is a lower alkylene radical, preferably a methylene or an ethylene radical; and compounds of the formula:

wherein each of R to R is an alkyl radical and R and R are preferably tertiary alkyl radicals having from 4 to 8 carbon atoms.

Typical specific hindered phenols useful in this invention include, for example, such compounds as:

The stabilizing amount of hindered phenol is generally in the range of from about 0.8 to about 3 moles per total moles of diazonium salt, and preferably in the range of from about 0.9:1 to about 1.7:1 moles.

The dye-forming components and other additives, when employed, are dispersed in the matrix polymer by any convenient technique, preferably by admixing all components in a common solvent. A particularly preferred solvent system comprises a mixture of a halogenated aliphatic hydrocarbon, especially ethylene chloride, and an alkanol, especially ethanol. The order of addition of the ingredients is variable, although it is preferred that acid stabilizers be added to the solution prior to the diazonium salts. Similarly, the amount of solvent is not critical, although it is preferred that the resulting solution contain from about to about 15 weight percent solids and preferably from about 8 to about 12 percent solids.

The resulting solution is then employed to cast or coat a film in accordance with generally known techniques. Although not essential, typically the film is coated on a suitable support such as a cellulose ester like cellulose acetate, polyethylene terephthalate, polystyrene, or paper, preferably coated with one of the above materials and alternatively, polyethylene or a polypropylene, or suitably subbed with, for example, barium sulfate and the like to provide a composite, light-sensitive photographic element. The solution should be applied to the support at a rate suflicient to provide an optical density, when developed, of between .8 and 3, with densities of from 1 to 2 being typically employed. If the density is less than .8 the resulting film will have a poor latitude. On the other hand, with densities in excess of 3 the image obtained after development will have too high a contrast to be useful for making half-tone reproductions.

The resulting light-sensitive photographic element can be exposed or developed in any conventional manner. As is pointed out above, however, those compositions wherein the yellow coupler is a l-hydroxy-Z-naphthamide are especially suited for development by the more conventional ammonia processes, whereas those compositions wherein the yellow coupler is a 2-acylamidophenol are especially suited for the more recently developed high pressure anhydrous ammonia development techniques.

The following examples are illustrative of the invention. All parts expressed are parts by weight.

EXAMPLE I A solution of 6.35 parts 2,5-diethoxy-4-morpholinobenzene diazonium fluoborate, 4.45 parts 4-(diethylamino) benzene diazonium fiuoborate, 1.50 parts 2-hydroxy-N-(2- methoxyphenyl)-3-naphthamide, 3.18 parts 2-hydroxy-N- (2,4-dimethoxy 5 chlorophenyl)-3-naphthamide, 2.32 parts 1-hydroxy-Z-naphthopiperidide, 3.07 parts zinc chloride, 3.07 parts 5-sulfosalicylic acid, 9.18 parts 2,2-methylenebis[6-(l-methylcyclohexyl) 4 methylphenol], 5.71 parts 2,2 dimethyl-4-isopropyl-7-tert-butyl-6-chromanol, and 63.10 parts cellulose acetate is prepared in a 4:1 ethylene chloride ethanol solvent system at 10 percent solids. The solution is then coated on a subbed poly(ethylene terephthalate) support at a rate sufficient to provide a density of 1.75 in the coated element. The photographic element is then dried. A first portion of the element is exposed through a step wedge incorporating .3 Log E density increments to a mercury arc lamp, rich in ultraviolet rays, and is then developed by contacting the exposed element with aqueous ammonia vapors. A second portion is exposed and developed in a similar manner, except that the exposure is made through the developed first portion. A third portion is exposed and developed in a like manner, except that the exposure is through the developed second portion. The evaluation of the three developed elements is summarized below in tabular form, illustrating the substantial preservation of contrast through the third generation print.

A solution of 2.54 parts 4-morpholinobenzene diazonium fluoborate, 1.00 part 2-hydroxy-N-(2-methylphenyl)- 3-naphthamide, 0.454 part 1hydroxy-2-naphthopiperidide, 0.60 part 5-sulfosalicylic acid, 1.12 parts 2,2-dimeth yl-4-isopropyl-7-tert-butyl-6-chromanol, 1.80 parts 2,2- methylenebis[6-(l-methylcyclohexyl) 4 methylphenol] and 12.50 parts cellulose acetate is prepared in a 4:1 ethylene chloride-ethanol solvent system at 9 percent solids, and the solution is coated and dried as described in Example I. Also employing procedures similar to those of Example I, a first portion is exposed and developed and a second portion is exposed through the first portion, and developed. The evaluation of these two developed por tions is summarized below in tabular form showing a substantial preservation of initial contrast.

OPTICAL DENSITY Portion EXAMPLE III A solution of 9.25 parts 4-morpholinobenzene diazonium fiuoborate, 5.72 parts 2-hydroxy-N-(2-methoxyphenyl)-3-naphthamide, 2.65 parts S-acetamido-Z-methylphenol, 3 parts 5-sulfosalicyclic acid, and 79.4 parts cellulose acetate is prepared in a 4:1 ethylene chloride-ethanol solvent system at 10 percent solids. The solution is coated and dried as described in Example I. Also employing procedures similar to those of Example I, a first portion is exposed and developed except that development is accomplished by exposure to high pressure anhydrous ammonia vapors and a second portion is exposed through the first portion and developed in a like manner. The evaluation of these two developed portions is summarized below in tabular form showing a substantial preservation of initial contrast.

OPTICAL DENSITY Portion We claim:

1. A light-sensitive azo dye-forming composition comprising:

(a) as a light sensitive diazonium salt component, a

benzene diazonium salt selected from the group consisting of (l) a 2,5-diloweralkoxy-4-morpholinobenzene diazonium salt and (2) a combination of 2,5-diloweralkoxy-4-morpholinobenzene and 4-(diloweralkylamino)benzene diazonium salts,

(b) as a blue coupler component, a coupler selected from the group consisting of a 2-hydroxy-N-(2- loweralkoxyphenyl)-3-naphthamide, a Z-hydroxy-N- (2,4 diloweralkoxy halophenyl) 3 naphthamide and mixtures thereof,

(0) as a yellow coupler component, a coupler selected from the group consisting of (l) a 1-hydroxy-N-loweralkyl2-naphthamide,

(2) a 1 hydroxy-N,N-diloweralkyl-2-naphthamide, and

(3) a 1-hydroxy-N,N-loWeralkylene-2-naphthamide,

(4) wherein the molar ratio of blue coupler to yellow coupler is from about 1.5 :1 to about 2.5:1, and also including an organic acid compound in an amount sufficient to prevent premature coupling in said composition.

2. A light-sensitive azo dye-forming composition as in claim 1, wherein:

(a) the diazonium salt component comprises at least one of each the the morpholinobenzene diazonium salts and the dialkylamino benzene diazonium salts in a molar ratio between the two salts of from about 1:1 to about 3:1 respectively,

(b) the blue coupler component is at least one of each of the dialkoxyhalophenyl-naphtharnide and the alkoxyphenylnaphthamide in a molar ratio between the two blue couplers of from about 1.5:1 to about 2:1, respectively,

(c) the yellow coupler component is one of the 1- hydroxy-Z-naphthamides,

(d) the molar ratio of said blue coupler to said yellow coupler is from about 1.75:1 to about 1.95:1, respectively, and

(e) the molar ratio of said blue and yellow coupler components to said diazonium salt component is from about 1:1 to about 1.521, respectively.

3. A light-sensitive azo dye-forming composition as described in claim 2 wherein the morpholinobenzene diazonium salt is 2,5-diethoxy-4-morpholinobenzene diazonium fluoborate; the dialkylaminobenzene salt is 4-(diethylamino)benzene diazonium fiuoborate; the dialkoXyhalophenylnaphthamide blue coupler is 2-hydr0xy-N-(2,4- dimethoxy-S-chlorophenyl)-3-naphthamide; the alkoxylphenylnaphthamide blue coupler is 2-hydroxy-N-(2-methoxyphenyl)-3-naphthamide; and the l-hydroxy-Z-naphthamide yellow coupler is 1-hydroxy-2-naphthopiperidide.

4. A light-sensitive azo dye-forming composition as described in claim 1 wherein the diazonium salt component is the morpholinobenzene diazonium salt; the blue coupler component is the N-(2-alkoxyphenyl)naphthamide; and the yellow coupler component is the l-hydroxy- Z-naphthamide; the molar ratio of said blue coupler component to said yellow coupler component is from about 1.75:1 to about 1.95:1, respectively, and the molar ratio of said blue and yellow coupler components to said benzene diazonium salt component is from about 1:1 to about 1.5 :1, respectively.

5. A light-sensitive azo dye-forming composition as described in claim 4 wherein the diazonium salt is 2,5-diethoxy-4-morpholinobenzene diazonium fluoborate; the blue coupler is Z-hydroxy-N-(Z-methoxyphenyl)-3-naphthamide; and the yellow coupler is 1-hydroxy-2-naphthamide.

6-. A light-sensitive diazotype reproduction composition comprising a matrix polymer having dispersed therein a dye-forming system as described in claim 1, an organic acid compound in an amount sullicient to prevent premature coupling of said dye-forming system and an acidic inorganic salt to brighten the azo dye when formed.

7. A light-sensitive diazotype reproduction composition comprising 100 parts by weight of a matrix polymer having dispersed therein from about to about 40 parts by weight of a dye-forming system as described in claim 2; from about 1 to about 6 parts by weight of an organic acid; and from about 0.5 to about 2 parts by weight of an acidic inorganic salt.

8. A light-sensitive diazotype reproduction composition comprising 100 parts by weight of a cellulose ester as a polymeric matrix; from about to about parts by weight of the dye-forming system as described in claim 3; from about 2 to about 5 parts by weight of S-sulfosalicyclic acid; and from about 1 to about 1.5 parts by Weight of zinc chloride.

9. A photographic element comprising a support having coated thereon a light-sensitive diazotype reproduction medium as described in claim 7.

10. A light-sensitive diazotype reproduction composition comprising 100 parts by weight of a matrix polymer having dispersed therein from about 20 to about parts by weight of a dye-forming system according to claim 4; and from about 1 to about 6 parts by weight of an organic acid.

11. A light-sensitive diazotype reproduction composition comprising 100 parts by weight of a cellulose ester as a polymeric matrix; from about 25 to about 35 parts by weight of the dye-forming system of claim 5; and from about 2 to about 5 parts by weight of 5-sulfosalicyclic acid.

12. A photographic element comprising a support having coated thereon a light-sensitive diazotype reproduction medium as described in claim 10.

References Cited UNITED STATES PATENTS 2,233,038 2/1941 Sus et a1. 96---91 2,298,444 10/1942 Weissberger et al. 9691 2,405,523 8/1946 Sease et al. 96.91X 2,485,122 lO/1949 Von Glahn et a1. 9691X 2,598,453 5/1952 Slifkin 9691X 2,617,726 11/1952 Kessels 9691X 2,893,866 7/1959 Haefeli 9691X 3,052,542 9/1962 Sulich 9691X 3,064,049 11/1962 COX 9691X 3,069,268 12/1962 Herrick 96-75X 3,113,025 12/1963 Bialczak 96-49 3,248,220 4/1966 Van Rhij 96-91 3,373,021 3/1968 Adams et a1. 96-75X FOREIGN PATENTS 937,510 9/1963 Great Britain 9691 OTHER REFERENCES Kosav, 1.: Light-Sensitive Systems, 1965, p. 223. Van der Grinten, The Photographic Journal, vol. 928, 1952, pp. 43-48.

NORMAN G. TORCHIN, Primary Examiner C. L. BOWERS, JR., Assistant Examiner US. Cl. X.R. 

